1. Field of the Invention
The present invention relates to a fixing roller which includes a porous material layer covering an outer peripheral surface of a core and a thin-walled metal sleeve covering an outer peripheral surface of the porous material layer
2. Description of the Related Art
In an image forming apparatus, such as a copying machine, a printer or a facsimile machine, as a fixing device for heating/pressing/fixing on a target object (a transfer member, a photosensitive sheet, a dielectric-coated sheet, etc.) unfixed toner image formed/supported, in conformity to intended image information, on the target object in a transfer manner (indirect manner) or a direct manner through an appropriate imaging process mechanism, such as an electrophotographic process, an electrostatic recording process or a magnetic recording process, there has been widely known a so-called two-roller type device arrangement comprising a thermal-fixing roller and a pressing roller.
In connection with this type of fixing roller, as disclosed in Japanese Patent Laid-Open Publication No. 2004-53924 (Patent Publication 1), the assigner of his application provided “a fixing roller production method comprising: a first step of preparing a porous body which comprises a core and a porous material layer formed to have at least closed cells and disposed in surrounding relation to an outer peripheral surface of the core, and machining the porous body to have an outer diameter equal to or greater than an inner diameter of a thin-walled metal; a second step of applying an adhesive onto at least one of an outer peripheral surface of the porous body and an inner peripheral surface of the thin-walled metal sleeve; a third step of containing the porous body and the thin-walled metal sleeve in a pressurized container to apply pressure thereon in such a manner as to allow the porous body to have an outer diameter less than an inner diameter of the thin-walled metal sleeve; a fourth step of, within the pressurized container, inserting the porous body into the thin-walled metal sleeve to form a sleeve body; a fifth step of taking the sleeve body from the pressurized container to cause expansion of the porous body so as to allow an outer peripheral surface of the porous body to be brought in close contact with an inner surface of the thin-walled metal sleeve; and a sixth step of solidifying the adhesive to bond the porous body and the thin-walled metal sleeve together.”. This method would produce a fixing roller capable of maintaining a usable state over a long period of time under the condition of being actually driven and rotated.
In the technique disclosed in the Patent Publication 1, a foamed silicone rubber sponge (hereinafter refereed to simply as “silicone sponge”) is used as an elastic layer. The silicone sponge has problems specific thereto, such as unevenness in cell size and indetermination in cell shape. Thus, in a fixing roller produced by the method disclosed in the Patent Publication 1, a region deformed by an action of an external force has the risk of occurrence of cell collapse. If cell collapse occurs, the durability of the fixing roller will deteriorate. Thus, there is a strong need for solving this problem.